Open Quantum System Theory of Muon Spin Relaxation in Materials
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| Format: | Preprint |
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2026
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| _version_ | 1866910168245075968 |
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| author | Arguelles, Elvis F. Sugino, Osamu |
| author_facet | Arguelles, Elvis F. Sugino, Osamu |
| contents | We present a non-Markovian theory of muon spin relaxation that treats the implanted muon as an open quantum spin coupled to a temporally correlated local magnetic environment. Using a Schwinger-Keldysh influence-functional formulation, we derive a stochastic equation of motion for the muon spin, in which the fluctuation kernel is fixed by the local-field correlation tensor, while the retarded memory torque is introduced through an effective phenomenological backaction kernel. In the appropriate limits, the theory reduces to standard Kubo-Toyabe descriptions. This enables quantitative, global analysis of zero-field (ZF) and weak longitudinal-field (LF) $μ$SR spectra beyond the strong-collision approximation. Applied to $\mathrm{Li}_{0.73}\mathrm{CoO}_2$, the model supports a decomposition into a quenched width and a Li-driven dynamical component within the adopted parametrization, and yields fluctuation rates approximately consistent with activated behavior over the intermediate-temperature window. The fitted memory parameter is most visible in the crossover between quasi-static and fast-fluctuation limits. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2603_23137 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Open Quantum System Theory of Muon Spin Relaxation in Materials Arguelles, Elvis F. Sugino, Osamu Materials Science Other Condensed Matter We present a non-Markovian theory of muon spin relaxation that treats the implanted muon as an open quantum spin coupled to a temporally correlated local magnetic environment. Using a Schwinger-Keldysh influence-functional formulation, we derive a stochastic equation of motion for the muon spin, in which the fluctuation kernel is fixed by the local-field correlation tensor, while the retarded memory torque is introduced through an effective phenomenological backaction kernel. In the appropriate limits, the theory reduces to standard Kubo-Toyabe descriptions. This enables quantitative, global analysis of zero-field (ZF) and weak longitudinal-field (LF) $μ$SR spectra beyond the strong-collision approximation. Applied to $\mathrm{Li}_{0.73}\mathrm{CoO}_2$, the model supports a decomposition into a quenched width and a Li-driven dynamical component within the adopted parametrization, and yields fluctuation rates approximately consistent with activated behavior over the intermediate-temperature window. The fitted memory parameter is most visible in the crossover between quasi-static and fast-fluctuation limits. |
| title | Open Quantum System Theory of Muon Spin Relaxation in Materials |
| topic | Materials Science Other Condensed Matter |
| url | https://arxiv.org/abs/2603.23137 |